Devices for recovering of oil and gas from long, horizontal and vertical wells are known from U.S. Pat. Nos. 4,821,801, 4,858,691, 4,574,691 and GB patent publication No. 2169018. These known devices comprise a perforated drainage pipe with, for example, a filter for control of sand around the pipe. A considerable disadvantage with the known devices for oil/and or gas production in highly permeable geological formations is that the pressure in the drainage pipe increases exponentially in the upstream direction as a result of the flow friction in the pipe. Because the differential pressure between the reservoir and the drainage pipe will decrease upstream as a result, the quantity of oil and/or gas flowing from the reservoir into the drainage pipe will decrease correspondingly. The total oil and/or gas produced by this means will therefore be low. With thin oil zones and highly permeable geological formations, there is further a high risk that of coning, i.e. flow of unwanted water or gas into the drainage pipe downstream, where the velocity of the oil flow from the reservoir to the pipe is the greatest.
When extracting oil from reservoirs by injection of steam or using combustion, the differential pressure can vary along the drainage pipe. Variations in differential pressure can be caused by an uneven distribution or propagation of injected steam and/or combustion heat in the reservoir. Fluids present in the reservoir formation, which fluids can be formation water, condensed steam and/or liquid hydrocarbons, are at or near their respective boiling points. Under such conditions, changes in pressure may cause the fluids to flash or boil to produce gas or steam. This may cause problems should the gas or steam reach the valves used for draining fluid from the reservoir into the production pipe, as many such valves are not able to close to prevent steam or combustion gas from entering the production pipe. In particular, if the differential pressure is relatively low, ingress of steam or combustion gas can lead to a “short circuit” of the injection pressure and the production pressure. This will cause the differential pressure to drop even further, which has a negative effect on the efficiency of the drainage process. The efficiency is determined by the amount of injected energy versus the produced oil volume.
A further result of areas with low pressure differential combined with high temperature, also termed hot spots, is that fluid with low viscosity from high temperature regions of the reservoir will dominate the inflow into the production pipe. In this way, the production pipe will have an undesirable inflow profile along its length.
A break-through of hot fluids, such as hydrocarbons and or water, at temperatures near their respective boiling points can cause the fluid to flash or boil inside the production pipe. If this occurs upstream of or in a down-hole pump this will have a detrimental effect on the operation of the pump and will result in a limitation of the draw down, that is, the pressure difference between the reservoir pressure and the pressure in the production pipe.
From World Oil, vol. 212, N. 11 (11/91), pages 73-80, is previously known to divide a drainage pipe into sections with one or more inflow restriction devices such as sliding sleeves or throttling devices. However, this reference is mainly dealing with the use of inflow control to limit the inflow rate for up hole zones and thereby avoid or reduce coning of water and or gas.
WO-A-9208875 describes a horizontal production pipe comprising a plurality of production sections connected by mixing chambers having a larger internal diameter than the production sections. The production sections comprise an external slotted liner which can be considered as performing a filtering action. However, the sequence of sections of different diameter creates flow turbulence and prevents the running of work-over tools operated along the outer surface of the production pipe.
Inflow control devices or autonomous valves as disclosed in the international publications WO 2009/088292 and WO 2008/004875 are robust, can withstand large forces and high temperatures, can prevent draw downs (differential pressure), need no energy supply and can withstand sand production. At the same time they are reliable, simple and very cheap. However, several improvements might nevertheless be made to increase the performance and longevity of the above devices.
When extracting oil and or gas from geological production formations, fluids of different qualities, i.e. oil, gas, water, are produced in different amounts and mixtures depending on the property or quality of the formation. None of the above-mentioned, known devices are able to distinguish between and control the inflow of oil, gas or water on the basis of their relative composition and/or quality. In particular, the known devices are not able to control variations in inflow into the production pipe due to variations of differential pressure caused by temperature variations. Said valves are also unable to control the effects of fluid flashing or boiling inside the production pipe.
The present invention provides an improved production pipe which aims to minimize problems relating to variations in inflow into the production pipe due to temperature variations. The invention further aims to reduce problems relating to fluids flashing or boiling in a production pipe.